Surprising News About Bicycle-Powered Electricity Generators

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That hourglass-shaped device is the PowerPac, an energy storage device meant to be powered by a human on a stationary bicycle. Conceived of by South African design firm Ideso, the PowerPac won a Red Dot Design Award in the “Best of the Best” category.

“Our aim was to create an aesthetically pleasing, user-friendly and functional design that marries the fluidity of cycling with dynamic power generation,” says Ideso MD, Marc Ruwiel. “It can be used by avid cyclists who can reduce CO2 emissions and generate their own electrical power, while enjoying a good workout at home.”

I’m all for people-powered electricity generators, and I would’ve loved to have one of these during the recent blackout, but something struck me in the copy: “…An average cyclist could fully charge the battery from empty with 80 minutes of cycling and 132Wh of charge/potential energy can be stored in the battery.” The “Wh” designation stands for watt-hour, and “132Wh” means you could power a 132-watt device for 1 hour. For 80 minutes of cycling to yield, say, just over two hours of light from a 60-watt bulb sounds like a low yield, doesn’t it? My first thought was, can that be right?

I did a little digging, and here’s what I found. It turns out hooking a bicycle up to something that directly powers a mechanical device is a fairly efficient way to generate energy. Rig a bicycle up to drive a sewing machine or a hand mixer and you get decent bang for your buck. But the second you get batteries and electricity involved, the efficiency drops way, way off. An article in Low-tech Magazine called “Bike powered electricity generators are not sustainable” explains why:

…Generating electricity is far from the most efficient way to apply pedal power, due to the internal energy losses in the battery, the battery management system, other electronic parts, and the motor/generator. These energy losses add up quickly: 10 to 35 percent in the battery, 10 to 20 percent in the motor/generator and 5 to 15 percent in the converter (which converts direct current to alternate current). The energy loss in the voltage regulator (or DC to DC converter, which prevents you from blowing up the battery) is about 25 percent. This means that the total energy loss in a pedal powered generator will be 42 to 67.5 percent….

And it even turns out that the bicycle itself has mechanical inefficiencies that suck up more energy:

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